A vehicle fuel system may include an evaporative emissions system designed to reduce the release of fuel vapors to the atmosphere. For example, vaporized hydrocarbons (HCs) from a fuel tank may be stored in a fuel vapor storage canister packed with an adsorbent that adsorbs and stores the vapors. At a later time, when the engine is in operation, the fuel vapors may be purged from the evaporative emissions system into an engine intake manifold for use as fuel. In some examples, the evaporative emissions system may be configured to store refueling vapors, running loss vapor, and diurnal vapors. However, in other examples, the evaporative emissions system and fuel system may be configured as a non-integrated refueling canister only system (NIRCOS). In such a system, the fuel tank is sealed, and fuel vapors are only routed to the fuel vapor storage canister during a refueling event. For example, a plug-in hybrid electric vehicle (PHEV) may include a NIRCOS due to limited engine run time. If the fuel tank were vented, prolonged electric mode driving (in which the engine is off and the vehicle is propelled with torque from an electric motor) may result in the fuel vapor storage canister becoming overloaded and fuel vapors being emitted to the atmosphere.
In order to seal the fuel tank from the fuel vapor storage canister, the NIRCOS may include a fuel tank isolation valve (FTIV) between the fuel tank and the fuel vapor storage canister. For example, the FTIV may be a solenoid valve under control of a pulse-width modulated signal. The FTIV may be at least partially opened to regulate fuel tank pressure during engine-on conditions and to prepare the fuel tank for refueling (e.g., during engine-off conditions). Typically, a pressure sensor is coupled to the fuel system (such as a fuel tank pressure transducer coupled to the fuel tank) in order to measure a fuel tank pressure. An additional pressure sensor may be included on the fuel vapor storage canister-side of the FTIV in order to monitor for degradation in the evaporative emissions system.
However, the inventor herein has recognized that including two pressure sensors in the NIRCOS may increase the cost of the system and lead to multiple points of degradation, as each sensor may independently degrade. Costs and complexity may be reduced by eliminating one of the sensors. However, including only the fuel tank pressure sensor (and eliminating the fuel vapor storage canister-side pressure sensor) would require the FTIV to be opened to test for degradation in the fuel vapor storage canister-side of the evaporative emissions system, which would not allow only refueling vapors to load the fuel vapor storage canister. In another example, eliminating the fuel tank pressure sensor would result in a lack of knowledge about the fuel tank pressure, which might degrade fuel tank pressure control when the engine is running as well as fuel tank depressurization during a refueling event.
The inventor herein has recognized that a single delta pressure sensor may be coupled across the FTIV, thereby reducing the cost/complexity of the NIRCOS and the overall cost of the vehicle while still enabling detection of both evaporative emissions system and fuel system degradation.
In one example, the issues described above may be addressed by a method, comprising: differentiating degradation between each of a sealed fuel tank, an evaporative emissions system, and a fuel tank isolation valve (FTIV) based on a differential pressure measured by a delta pressure sensor coupled across the FTIV, the FTIV positioned between the sealed fuel tank and the evaporative emissions system. In this way, a single delta pressure sensor may be used to identify degradation in the evaporative emissions system, the fuel system, and/or the FTIV.
As one example, a first pressure port of the delta pressure sensor may be fluidically coupled to a conduit between the FTIV and the sealed fuel tank, and a second pressure port of the delta pressure sensor may be fluidically coupled to the conduit between the FTIV and a fuel vapor storage canister of the evaporative emissions system. With no restricting components, such as valves, present between the sealed fuel tank and the first pressure port and/or the fuel vapor storage canister and the second pressure port, the differential pressure measured by the delta pressure sensor indicates a relative pressure (or vacuum) of the evaporative emissions system as well as a relative pressure (or vacuum) of the sealed fuel tank. For example, the relative pressure (or vacuum) of the evaporative emissions system is relative to a pressure of the sealed fuel tank, and the relative pressure (or vacuum) of the sealed fuel tank is relative to a pressure of the evaporative emissions system. In this way, a change in differential pressure measured by the delta pressure sensor may be used to detect evaporative emissions system degradation during, for example, a canister-side engine off test, and the relative pressure (or vacuum) of the sealed fuel tank may be used to detect and differentiate between fuel system and FTIV degradation, such as when the fuel tank is not completely sealed. With only one delta pressure sensor included for both the evaporative emissions system and the fuel system, vehicle costs, complexity, and points of degradation may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.